Doctors and policymakers in the rich world are increasingly worried about loneliness. Campaigns to reduce it have been launched in Britain, Denmark and Australia. In Japan the government has surveyed hikikomori, or “people who shut themselves in their homes”. Last year Vivek Murthy, a former surgeon-general of the United States, called loneliness an epidemic, likening its impact on health to obesity or smoking 15 cigarettes per day. In January Theresa May, the British prime minister, appointed a minister for loneliness.

And

Researchers define loneliness as perceived social isolation, a feeling of not having the social contacts one would like. Of course, the objectively isolated are much more likely than the average person to feel lonely. But loneliness can also strike those with seemingly ample friends and family.

And

Researchers have three theories as to how loneliness may lead to ill health, says Nicole Valtorta of Newcastle University. The first covers behaviour. Lacking encouragement from family or friends, the lonely may slide into unhealthy habits. The second is biological. Loneliness may raise levels of stress, say, or impede sleep, and in turn harm the body. The third is psychological, since loneliness can augment depression or anxiety.

Read more at the Economist (paywall)